Gorham’s Cave Complex in Gibraltar has been home this month to the world’s largest known roost of crag martins. Researchers studying the wintering population of the species (Ptyonoprogne rupestris) at the UNESCO World Heritage Site were reported to have been surprised by an unprecedented arrival of these birds during the early part of November.
According to the Gibraltar Government, during one of two weekly counts of the birds entering the caves in the evening, the count exceeded 5,700. “This figure could represent up to one per cent of the European post-breeding population, which is remarkable, and makes this the largest known roost of this species in the world.”
Previous counts undertaken in recent years had reached a maximum of 3,600 birds, which was comparable to counts in the 1970s (done by some of the researchers of the current project) that placed the winter roost at 2,000 to 3,000 birds.
It was believed that wintering numbers had dropped significantly but the government reports that no accurate counts had been completed until the current project resumed three years ago. “It is known that the birds wintering in the caves come from as far as the French Pyrenees and the Italian Alps.”
The project research team comprises scientists and co-workers from the Gibraltar National Museum, Gibraltar Botanic Gardens and Gibraltar Ornithological & Natural History Society, working jointly as a University of Gibraltar project.
They believe there may be various reasons for the observed increase… “These birds may have had an exceptionally good breeding season in Europe or a recent spell of bad weather in the Iberian Peninsula may have pushed greater numbers than usual south. Another explanation, in part at least, may well be the protection offered by the Gorham’s Cave Complex since it became a UNESCO World Heritage Site in 2016. These birds are able to rest and sleep undisturbed as the roost is nowadays carefully protected.”
The crag martin roost was first noticed in the late 18th century when the Reverend John White reported their presence to his brother, renowned naturalist Gilbert White of Selborne. “These observations contributed to the understanding of the phenomenon of bird migration at that time. The crag martin roost is an ancient one, the remains of these birds having been found in Neanderthal contexts dating to over 100,000 years ago.”
Commenting on the latest results, the minister with responsibility for the environment and the World Heritage Site Professor, John Cortes said, “It’s really exciting to see how protection can help potentially vulnerable species. I have a very personal interest in these birds as I was part of the team counting and ringing them in the seventies.
“These birds have used this site for millennia and I’m proud that we are contributing positively to their current success. This case shows how important the protection offered by our World Heritage Site translates from cultural to natural protection. Protecting the site doesn’t just include the Neanderthals and their remains but all life currently using it – it’s a perfect example of total conservation.”
Photos courtesy of HM Government of Gibraltar
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